21671831 has 2 divisors, whose sum is σ = 21671832. Its totient is φ = 21671830.

The previous prime is 21671813. The next prime is 21671851. The reversal of 21671831 is 13817612.

Together with previous prime (21671813) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21671831 is a prime.

It is a super-2 number, since 2×21671831² = 939336517785122, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21671794 and 21671803.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21671801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10835915 + 10835916.

It is an arithmetic number, because the mean of its divisors is an integer number (10835916).

Almost surely, 2^21671831 is an apocalyptic number.

21671831 is a deficient number, since it is larger than the sum of its proper divisors (1).

21671831 is an equidigital number, since it uses as much as digits as its factorization.

21671831 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 29.

The square root of 21671831 is about 4655.3013865914. The cubic root of 21671831 is about 278.8037013712.

The spelling of 21671831 in words is "twenty-one million, six hundred seventy-one thousand, eight hundred thirty-one".